1. Field of the Invention
This invention relates to drip irrigation; and more particularly, to a method for making drip irrigation lines in which the drippers are molded and simultaneously bonded to a flexible sheet used to make the supply pipe.
2. Description of the Prior Art
Drip irrigation systems usually include a continuous irrigation water supply line with emitter-type drippers installed along the line, usually at regular intervals. Irrigation water flows through the supply line under pressure, and a small amount of water continuously drips out at the intervals where the drippers are located. Drip irrigation has proved to be highly successful in producing greater growth of vegetation for the same amount of water, when compared with conventional irrigation techniques.
A number of different drip irrigation systems have been used in the past. They vary from the cheapest and simplest of systems, namely, a hole in the wall of the water supply line, to expensive and complex multi-component dripper units.
There is a need for a low cost dripper system having reliable performance in terms of uniform flow rates and resistance to clogging at operating pressures of say between 7 to 40 psi. A single hole in the water supply line may be the cheapest of drip systems, but such an approach is not satisfactory in most cases. The hole in the pipe wall must be of minute size to produce the desired dripping rate. However, the required hole size is so small that blockage is almost inevitable at a number of places along the line, even with filtering. Moreover, a minute hole limits the practical operating pressure in the supply line to less than about 10 psi. At higher, more desirable line pressures of above say 15 psi, the water jets or sprays through the holes in the pipe wall. By reliably running a drip irrigation system at a higher oeprating pressure of say 15 psi, longer supply lines can be used; more output, in terms of gallons of water per hour, is produced; and the system can work on undulating ground (up and down slopes) as well as on reasonably flat ground.
A large number of more sophisticated drip irrigation systems have been developed for the purpose of overcoming the problems inherent in a single hole in the wall-type of irrigation line. A common and successful approach involves use of separate drip emitters or drippers installed in or on the supply pipe. The dripper taps off a portion of the water flowing in the supply line and passes the water through a labyrinth or other meandering or circuitous path that produces a large pressure drop in the water and discharges it at a uniform drip rate. Generally, such pressure-reducing labyrinthine drippers are successful because they use a large enough hole in the supply pipe and a wide enough passage through the labyrinth to avoid clogging in most cases, while they can be used at higher line pressures.
There is a need to reduce the capital, material, and labor costs of manufacturing high-quality emitter-type dripper lines. Emitters usually consist of two to four molded sections assembled together and then mounted or inserted into the supply pipe. The cost of assembly and mounting of the dripper is a substantial proportion of the total cost of the dripper line. Emitter-type systems also can involve expensive molding and bonding techniques and materials.
In addition to the need for reasonably low capital, material, and labor costs, it is also desirable that emitter-type systems be capable of use with thin wall supply pipe as well as more permanent heavy wall pipe. Orchards and vineyards, for example, commonly use permanent drip irrigation systems, whereas cheaper thin wall pipe can be used for temporary drip irrigation sites.
There is also a need to ensure that the emitter-type dripper system will operate reliably during use, avoid clogging in most cases, and be capable of use at higher line pressures.
The present invention provides a method for making an emitter-type drip irrigation line with inexpensive injection molding techniques and materials which reduce the capital, material, and labor costs of making the dripper line. The resulting dripper line preserves the advantages of the high quality emitter-type systems and is reliable in use. In addition, the method can be used for making low-cost, thin-wall dripper lines as well as more permanent dripper systems made from heavy wall film.